Telecommunication systems typically include redundant circuit elements which facilitate continuous system operation even upon encountering a defect in an active circuit element. When a defect is detected, the defective element may be replaced with an equivalent redundant element, thus allowing the system to continue proper operation. Systems implementing redundant circuit elements benefit from devices facilitating switching between normal and redundant circuit elements.
Conventional line circuits may switch between normal and redundant line circuit elements using a mechanical relay to accomplish the switching function. A problem with this approach is that mechanical relays are typically large and bulky. In addition, they are more prone to failure and often consume more power than solid state elements. Another approach to switching between normal and redundant line circuit elements is to use a solid state relay with an isolated control input. A disadvantage of this approach is that the photo diode typically used to isolate the control line from the input line generally requires a large current to hold the switch closed. These solid state relays, therefore, may consume more power than is desirable.